Retorts have been widely used for in-container preservation of foodstuffs, either for pasteurization or sterilization processes. A retort generally includes a pressure vessel for receiving containers containing foodstuffs arranged on trays or baskets that are stacked on pallets or other types of carrier structures. The sterilization/pasteurization of the food products can occur by applying heating media to the food product containers, including, for example, super-heated steam or hot water. Such heating media can be applied by spraying onto the stacked containers. Alternatively, the heating media can be introduced into the retort vessel to immerse the containers holding the foodstuffs.
Rather than utilizing a static system wherein the containers are held stationary within the retort vessel during pasteurization or sterilization, an agitating retort can be employed. Agitation of the food products during pasteurization/sterilization in a retort can result in a shorter processing time and improve the quality and presentation of the food product. Semi-convective products and those containing particulates especially benefit from agitation. The improvement in the presentation of the food product stems in part from a lower thermal load or burden having to be applied to the food product to accomplish the required level of pasteurization or sterilization.
The agitation of food products in a retort has been accomplished by different systems. In one system the pallets/carriers of foodstuff containers are loaded within a drum positioned within the retort vessel. The drum is rotated about its longitudinal axis to produce end-over-end agitation of the food product. Although end-over-end agitation is quite effective, it does require a drive system to rotate the drum as well as a support structure for the drum during rotation within the retort, as well as systems for introducing the processing fluid into the rotating drum.
Another type of agitation retort relies on linear agitation of the food product. By moving the food product back-and-forth over a relatively short distance within the retort, the change in direction at the end points of the back and forth travel results in deceleration and acceleration forces in the containers that induce an agitation effect on its content. The effect of linear agitation is less than that achievable by end-over-end agitation; however, in many cases such “light agitation” can sufficiently reduce the processing time and/or avoid clumping of the product, to be warranted relative to simply static thermal processing of the food product.
A typical linear agitation system includes the drive mechanism consisting of a crankshaft rotated by a motor. Both the crankshaft and motor are located outside one end of the retort. A connecting rod system connects a crankshaft to the retort pallet/carrier. Relatively heavy duty drive systems are required in these types of linear agitation systems, including the need to counterbalance and smooth out the forces applied to the food product by the rotating crankshaft. This counterbalancing is typically accomplished through the use of one or more flywheels.
Linear agitation of food products within a retort with a crank mechanism located outside of the retort results in sinusoidal movement of the food product. In this regard, the maximum acceleration or deceleration is achieved at only two points during rotation of the crank mechanism. Acceleration of the food product is defined by the formula: ω2*R*sin(α). In this equation, ω equals the rotational speed (in rad/s); R is the crank radius (meters); and α is the rotational angle (rad).
To achieve higher acceleration for a given crankshaft radius, the rotational speed of the crankshaft needs to be increased. For instance, for a crankshaft radius of R=0.075 m, to achieve an acceleration of 0.4 g (4 m/s2), a rotational speed of 7.30 rad/seconds or 69.7 revolutions per minute (RPM) is required. A challenge in linear agitating systems is to achieve a sufficiently high acceleration of the food product, but at the same time limiting the number of revolutions or cycles per minute of the crankshaft mechanism and also minimizing the amount of energy consumed. As noted above, typically in linear agitation systems, a flywheel is needed to store the kinetic energy of the moving mass within the agitating retort.
The present disclosure seeks to address the drawbacks of existing linear agitating systems by providing an inherently balanced linear agitating system accomplished by moving food product sets in opposite reciprocating directions to each other and requiring modest operating energy.